The present invention relates to a method for preventing a surging of fluids in a tank of a tank truck, during transportation. Said tank truck having a drive train comprising an internal combustion engine, a clutch device and an automatic or automated manual transmission.
It is well known that fluids in a partly filled up tank of a tank truck surges around in the tank during transportation. The surging in the tank influences the vehicle's driving performance. Due to the inertial reactions of the fluid, for example during accelerations, retardations, and transportation during poor conditions, such as bumpy and uneven roads, low frequency oscillations of the vehicle might occur. The acceleration, retardation, and transportation with the vehicle becomes uneven as the longitudinal oscillations acts with or against the wanted acceleration or retardation respectively. These longitudinal oscillations of the vehicle are apprehended as very unpleasant by the driver of the vehicle and are also unwanted seen from a safety point of view.
There are several known solutions to dampen the problem with surging in the tank and low frequency longitudinal oscillations of the vehicle. The most common one is to build in some sort of surging inhibiting device in the tank. Such a surging inhibiting device is usually supposed to divide the tank volume in smaller sections, so that the movement of the fluid decreases. There are several different forms of surging inhibiting devices, for example in WO 87 01101 an Ω-shaped anti-surging element is suggested, which can be fitted inside a tank. There are several problems with surging inhibiting devices like this one. Firstly, they can not prevent the occurring of the low frequency longitudinal oscillations of the vehicle. These solutions can only dampen them. Secondly, the material usage for these solutions is mostly quite high and makes the vehicle heavier and takes up important transport room. Thirdly, the extra structure in the tank makes the tank much harder to clean, which especially in a tank for provisions is a problem.
In DE 10 2005 021 415 a method is suggested to dampen longitudinal oscillations of a tank truck, wherein the oscillations are derived from a fluid in the tank of the tank truck. The method uses the realization that an oscillation counteracting the oscillation derived from the fluid can neutralise the unwanted vehicle oscillations derived from the fluid.
The present invention uses, according to an aspect thereof, the realisation that a preventing of the surging in the tank, would improve the safety for tank trucks. With known methods, the unwanted vehicle oscillations must occur before they can be neutralised, which means that it still will be a period of time as the tank truck is exposed to the low frequency longitudinal oscillations.
Thus, it is desirable to suggest a method which prevents the occurring of low longitudinal oscillations of a tank truck, derived from surging in a partly filled up tank. It is also desirable to suggest a device for controlling the drive train of such tank trucks.
The present invention relates, according to an aspect thereof, to a method for preventing a surging of fluids in a tank of a tank truck having a tank for transportation of fluids. The drive train comprises an internal combustion engine, a clutch device and an automatic or automated manual transmission. Further the drive train is controlled by an electronic control unit, which is prepared to receive input data from detecting means for detecting a tank driving mode and sensing means for sensing a load status of the vehicle.
The inventive method according to an aspect of the invention comprises the steps of:                detecting a tank drive mode,        calculating a launch gear, and        limiting the torque gradient of the clutch device.        
The detecting means for detecting a tank drive mode can for example be a manual device controlled by a driver, for example a button, an arm or any other kind of switch inside the drivers cabin of the tank truck. The driver activates the tank drive mode through the switch when the tank truck is driving with a partly filled tank. Another example of a possible detecting means can be a sensor, which detects if a tank load is connected to the truck and preferably also detect that the tank is partly filled. The sensing means sends input data to the ECU when a tank load, i.e. a tank drive mode, is detected. The detecting means for detecting a tank drive mode can also be an ECU which activates the tank driving mode upon detection of a predetermined vehicle behaviour. Said mentioned different detecting means for detecting a tank drive mode can be combined. Said automatic transmission can be a step geared planetary gear based transmission. Said automated manual transmission (AMT) is a step geared transmission with a counter shaft arrangement.
A launch gear for the tank truck is calculated from the tank truck data, such as drive train specifics and the mass of the tank truck together with the data collected from the sensing means. The aim is to find a launch gear that is as high as possible, but still can offer enough torque to launch the tank truck. In this way a smooth launch of the tank truck will be possible. Mostly this will result in that the start gear is one gear higher than with a launch with a correspondent solid load. For example: A 12 speed, 40 ton truck, would normally launch from its second gear. With a tank drive mode activated the same truck would launch from its third gear.
To further facilitate a smooth start of the tank truck and additional a smooth gear change the torque gradient of the clutch device is limited. The clutch device can be a friction clutch or a torque converter of any kind that fulfil the purpose as a disengagable/engagable torque transmitting element in a drive line. Due to the limited torque gradient the clutch device will disengage and engage slower and therefore enclose a longer period of slip during its disengagement and engagement. Hence a smoother transition from a still standing position by launching the tank truck and between the different gears during a gear change will be realized.
In a further embodiment of said invention and after said step of detecting a tank drive mode and prior to calculating a launch gear the inventive method can further comprise the step of:                sensing a load status of the tank truck.        
As the ECU receives the input data from the detecting means that a tank load is present, the sensing means for sensing the load status of the tank truck is called up by the ECU and the ECU receives input data from the sensing means. The sensing means can alternatively also have the function as a detecting means. The sensing means can for example be sensors in the tank, and that said sensors can identify the load, the fill level and preferably other fluid specifics. Such sensors could be pressure sensors and/or fluid presence sensors and/or fill level sensors and/or viscosity sensors and/or alternative sensors, which could sense the wanted data. Alternatively the sensing means can be an information device, in which an operator manually or automatically specifies the load data, such as; fill level and/or density and/or viscosity and/or any other relevant data. The manual specification of the data can for example be done through a keyboard, a touch screen or the like and an semi-automatically or automatically specification in the information device can for example be done through scanning of a barcode or the like, or be transmitted to the device. A further possibility is a device in combination with sensors.
The inventive method embodiments suggest a tank drive mode to control a drive line of a tank truck. The method will during launch and travel, minimize or even avoid dangerous surging of a fluid in the tank, causing low frequency longitudinal oscillations of the tank truck. Due to the inventive method safety for the driver of the tank truck and the fellow road-users is significantly increased. Further, a cleaning of the tank is simplified, since the need for anti-surging elements in the tank is reduced.
In a further embodiment according to an aspect of the inventive method the following additional steps are suggested:                limiting the engine torque gradient, and/or        reducing the gear change velocity in a vehicle acceleration, and/or        disabling a kick down function.        
Due to that the engine torque gradient is limited a driver's sudden and fast and/or large difference in demanded torque will not result in a corresponding engine torque increase or decrease. Instead the ECU will control the engine torque in such a way that it slowly increases or decreases until it reaches the, from the driver or from a cruise control, demanded torque. A softer acceleration or retardation, which leads to less surge in the tank will be the result. A smoother gear change will be achieved through the suggested transmission control, which reduces the gear change velocity of the tank truck during vehicle acceleration. The gear change will be performed earlier than if the truck would drive with a solid load. With earlier is meant; at a lower engine speed and as a result thereof at a lower velocity of the tank truck. For example: A 12 speed, 40 ton truck, would have its gear change engine speed at 1900 rpm, for a three step gear change, and at 1700 rpm, for a two step gear change, and at 1550 rpm, for a one step gear. The same truck with a tank drive mode activated, would avoid a three step gear change, and have it gear change speed at 1600 rpm, for a two step gear change, and at 1450 rpm, for a one step gear change.
A third measure is suggested, which disables a “kick down” function. This, since the “kick down” function endeavors a fast change in torque, which contradicts the soul of this invention. The suggested additional steps are independent of each other; therefore one of the additional steps or any combination of the additional steps can be included in the tank drive mode.
If the mass of the load is unknown through the sensing means a calculation of the mass of the load must be done by the ECU. Known methods to calculate the mass of the load during launch are based on the relationship between acceleration and driving force or acceleration, vehicle speed and opening of a throttle valve. Such a method collects data from the engine and the drive train during a fix and mostly short time period. Due to the inertial reaction of the fluid such a method will end up false if this is not included in the calculation.
An improved method to calculate the mass of the tank truck during the launch of the vehicle is suggested. The improved method suggests that in addition to the relation between engine data and drive train data respectively and the vehicle acceleration and/or speed and/or throttle opening, a compensation for the inertial reaction of the fluid is done. This could be a longer sensing period for collecting data for the calculation, and that the longer sensing period permits a compensation of the inertial reaction of the fluid.
An extension of the inventive method involves measures for reducing the occurrence of surging during retardation. The extended method comprises the steps of:—limiting the brake gradient, caused by an auxiliary braking system of the tank truck, and/or                reducing the gear change velocity of the tank truck during an retardation and/or        avoiding high engine rotational speeds and or—disabling a brake mode.        
By reducing the brake gradient of an auxiliary braking system of the tank truck a smoother engagement of the brake will be achieved and the risk of surging in the tank, due to the braking will be reduced. An auxiliary braking system is for example a retarder, an exhaust braking system or engine braking system (engine compression brake). A limiting of the primary braking system (service brakes) is not recommended, due to safety reasons. The reduced gear change velocity of the tank truck during retardation results in a smoother gear change, i.e. the gear change will be performed later than normal in order to decrease the difference in torque when the clutch device opens and closes. By avoiding high engine rotational speeds the risk of exposing the drive train to sudden torque changes will be decreased and the risk of surging in the tank will be reduced. In an alternative embodiment of the invention a special automatic braking program can be hindered to be activated in order to limit the risk of surging in the tank. Such a special automatic braking program when activated can typically be arranged to maximize engine braking by using high engine rotational speeds, i.e. the transmission down shifts as many gear steps as possible.
Even though the inventive method aims, according to an aspect thereof, to minimize the occurrence of longitudinal oscillations due to surging in the tank, it is possible that such oscillations occur due to other circumstances. Therefore, it is suggested that an aspect of the inventive method as an alternative comprises the steps of:                detecting low frequency longitudinal oscillations of the tank truck, derived from the fluid in the tank, and—calculating the timing and intensity of the next change in torque, with the requirement that the next change in torque will counteract with the low frequency longitudinal oscillations of the tank truck.        
A detection of the low frequency longitudinal oscillations of the tank truck can be made in the drive train. In today's vehicles a plurality of sensor are present in the drive train, to monitor the behaviour of the drive train. For example the sensors are present in the engine, the transmissions, the differential and/or the wheels. Also the low frequency longitudinal oscillations of the tank truck can be traced in the information from these sensors. The low frequency longitudinal oscillations of the tank truck will influence the drive train, so that also the drive train shows these low frequency oscillations. The low frequency oscillations in the drive train, derived from surging in the tank, can be separated from other oscillations in the drive train, for example derived from the engine or the transmission since these oscillations show a much higher frequency. Thus, the information from the sensors can be analyzed in the ECU and when low frequency oscillations, derived from the fluid in the tank is found, the ECU calculates the timing and intensity of the next change in torque, so that this change counteract with the low frequency oscillations in the drive train. Such a counteraction can contradict the conditions of the tank drive mode. The ECU can therefore in a situation with low frequency longitudinal oscillations of the tank truck overrule previous conditions to be able to counteract the low frequency oscillations. For example, an abrupt and sudden disengagement or engagement of the clutch device can be allowed. In an alternative embodiment said plurality of available sensors can be used for comparison of engine output torque and vehicle acceleration. If the fluid in the tank is moving the engine torque and the vehicle acceleration will walk out of step. This can be used for detection of a surging fluid in the tank.
To further improve the inventive method it is suggested that the method comprises the steps of:—storage of detected and calculated data in a storage means, and                the electronic control unit accessing the data in the storage means instead of detecting and/or calculating new data when the tank circumstances are unchanged, and—replacing existing data in the storage means, when new data has been detected, and        recalculating the data for the tank drive mode when detected data has changed.        
According to the suggested steps of the inventive method the detected and calculated data is stored in a storage means, such as a RAM, and can at any time be accessed by the electronic control unit to write new data or read saved data. As long as the tank circumstances are unchanged the data from the storage means is preferably used. When new data has been detected, it will replace the previous data in the storage means and the tank drive mode data, such as launch gear and gear change patterns are recalculated based on the new data, whereupon the recalculated data is stored in the storage means.
In a variant of the inventive method an inlet or an outlet from the tank is automatically detected. Advantageously the, in the tank filled up volume or the, from the tank drained off volume is detected by sensing means. In this way the ECU will always sense if a volume of the fluid in the tank has changed and therefore have to recalculate new values, such as launch gear and gear change patterns. Especially in tank trucks that are filled and/or drained at several stations this would be a preferred feature. Such tank trucks could be tank trucks for milk transportation or heating oil for private houses. These trucks may already be equipped with such detecting/sensing means and these could then be connected with the ECU to communicate the detected values.